Effect of magnetism on lattice dynamics in FeSe using high- resolution inelastic X-ray scattering

村井 直樹  ; 福田 竜生  ; 中島 正道*; 河村 光晶*; 石川 大介*; 田島 節子*; Baron, A.*

Murai, Naoki; Fukuda, Tatsuo; Nakajima, Masamichi*; Kawamura, Mitsuaki*; Ishikawa, Daisuke*; Tajima, Setsuko*; Baron, A.*

The discovery of high- superconductivity in iron-based superconductors (FeSCs) has marked the beginning of a new era in superconductivity research. Many of the properties in FeSCs arise from the intricate interplay among spin, orbital, and lattice degrees of freedom. In particular, the interaction between structure and magnetism, often referred to as magnetoelastic coupling, is one of the most interesting topics in FeSC investigations, as it is increasingly recognized that these two degrees of freedom significantly impact each other. Here, we report an inelastic X-ray scattering investigation of phonons in FeSe. Comparing the experimental phonon dispersion with density functional theory (DFT) calculations in the nonmagnetic state, we found a significant disagreement between them. Improved overall agreement was obtained by allowing for spin polarization in the DFT calculations despite the absence of magnetic order in the experiment. This calculation provides a reasonable starting point for understanding the lattice dynamics of FeSe in close proximity to the magnetic phase. We will discuss the current state of our analysis relating the underlying magnetism of FeSCs to the phonon dispersion.